Modern communication standards such as UMTS/WCDMA or CDMA2000 place great demands on regulation of the output power from a transmitter. To match the accuracy of an output power or of a sudden change in the output power to the requirements and stipulations of the UMTS standard, it is often desired to implement power regulation in 1-dB steps with an accuracy of 0.1 dB within the transmission path in part of the 70 dB dynamic range of the output signal. Consequently, amplifiers in a transmission path require an accuracy of 0.1 dB for all amplifier settings over a dynamic range from 0 dB to −24 dB of the maximum output power. An error between the actual gain and the nominal gain is meant to be only 0.1 dB in the indicated dynamic range. At the same time, it is necessary to ensure sufficient linearity for the gain in the transmission path over the entire dynamic range.
The demanded linearity and accuracy over the dynamic range can be achieved by voltage controlled amplifiers (VGA, voltage-controlled gain amplifier) only with considerable complexity. For economic reasons, therefore, programmable amplifiers (PGC, programmable gain amplifier) are increasingly used in a transmitter's transmission path. The demanded dynamic range and the current drawn mean that it is also expedient to regulate the gain both in the transmission path's baseband and in the radio-frequency range of the transmission path using the amplifiers therein.
However, production tolerances and environmental influences make it more difficult to achieve the demanded error between the actual gain and the nominally set gain for the radio-frequency amplifiers. Thus, the error is approximately ±0.3 dB instead of the demanded 0.1 dB for radio-frequency amplifiers. A gain can thus be set only to an accuracy of 0.6 dB. For a smaller error, it is therefore necessary to calibrate the amplifier step sizes of the radio-frequency amplifiers in the transmission path.